The present invention generally relates to air purification systems, and more particularly, to an air purification system using ultraviolet light emitting diodes (LED) and photocatalyst-coated supports.
The use of recirculated air may be common within inhabited enclosures. In some cases, airflow may be necessarily recirculated to provide breathable air where air external to the enclosure may not be viable. In other cases, it may be more economical to use recirculated air which has already been adjusted to the correct temperature and humidity. For example, pressurized cabins in aircraft may commonly recirculate a portion of the air rather than try to circulate only external air into the cabin. One result of using recirculated air is that organic contaminants may increase in concentration and may be passed to the inhabitants of the cabin.
One approach to removing contaminants from airflow is to use a photocatalytic air cleaner on airflow. It may be known to use for example, mercury vapor lamps to irradiate a photocatalyst in contact with airflow. Lamps may produce a heterogeneously distributed intensity across a photocatalyst. This may result in portions of the airflow which are less well treated, and still contain contaminants. Mercury vapor lamps may also be commonly made of glass or quartz, and, therefore not useful in environments where mechanical shock might result in their shattering. In addition, the use of lamps may result in insufficient energy absorption by the photocatalyst to provide effective catalysis. This can occur if the emission spectrum of the lamps does not overlap with the absorption spectrum of the photocatalyst.
In some purification systems, titanium dioxide based photocatalysts may be employed. The absorbance of titanium dioxide for photocatalysis drops rapidly with increasing wavelength, and is negligible above 410 nanometers. At wavelengths at which the photocatalyst does not absorb light, no reaction will occur, so use of a light source whose emittance spectrum overlaps poorly with the absorption spectrum of the photocatalyst can result in poor efficiency. It may be desirable to operate a photocatalytic device using a light source which has a wavelength higher than that normally absorbed by titanium dioxide. In some cases, the absorbance spectrum of titanium dioxide may be shifted to higher wavelengths by, for example, doping titanium dioxide with nitrogen or carbon. The effectiveness of titanium based photocatalysts may be short lived as the doped element may degrade quickly and the titanium dioxide is again ineffective at wavelengths above 410 nm.
As can be seen, there is a need for an air cleaning system that may provide efficient and evenly distributed photocatalysis in airflow.